This invention relates to engine exhaust manifold assemblies, and particularly to the attachment of dual wall, air gap manifold runners to the port flange of the manifold.
Exhaust manifolds are formed of what is commonly called a "log," which forms the common gas flow chamber, and a plurality of runners which form the individual flow passages from the engine cylinders to the log. In recent years manifolds have been formed more and more of lightweight, stamped metal such as stainless steel rather than the prior heavy castings that were the standard structure. More recently, air gap manifolds have been devised in order to allow quick internal temperature rise of the manifold, for quick activation of the downstream catalytic converter. Air gap manifolds have an inner tubular liner and an outer tubular jacket generally spaced from each other, to define the air gap between them. The inner liner typically has a thickness less than that of the jacket, enabling even more rapid temperature rise of the liner. The liner and the jacket are often each formed of a clamshell type arrangement. That is, the liner is formed of two half shells secured together along their longitudinal edges, and the larger jacket likewise is formed of two half shells secured together along their longitudinal edges. Connection of the air gap manifold runners to the port flange presently presents a production problem. Specifically, problems arise with attachment of the ends of the jacket and the liner to each other at the port flange, as well as attachment of the jacket and liner to the manifold port flange. At least one manufacturer presently foregoes attachment of the liner to the port flange, leaving the liner to float, but this is not considered advisable. One problem area with attachment of the liner can result because of the potential for burning through the liner during the welding step. Among prior known methods of attachment of these members, an experimental adapter sleeve has been tried by the assignee, by which, with three annular welding seams, the jacket and liner can be secured to each other, the jacket and liner secured to the inside of the adapter sleeve, and the adapter sleeve secured to the port flange as shown in FIG. 6 hereof. However, this technology resulted in problems. Specifically, when TIG welding the liner and the jacket together, burn-through was a significant concern since it results in stress concentration and possible later breakage of the components. Secondly, the connector cup stamped into the adapter sleeve for fitting over and around the liner and jacket ends was often difficult to actually fit onto these liner and jacket ends. Thirdly, making all of these welds effective on each unit was costly and time consuming. Fourthly, any extra filler weld on the outermost weld seam could cause interference with the adjacent bolt socket for the manifold flange. Fifthly, if there was a faulty weld, exhaust gases could enter the air gap with definite negative results. Consequently, this prior experiment was not considered successful.